Field of the Invention
The present disclosure relates to a technique for removing shade in a captured image.
Description of the Related Art
Mobile terminals, such as smartphones and tablet personal computers (PCs), having advanced information processing functions are becoming more and more popular nowadays. These mobile terminals have a camera and an image capture function. It is becoming increasingly common to capture an image of a document on a paper medium using such a camera function of a mobile terminal, and store image data of the captured image into a memory of the mobile terminal. Additionally, the combination of a mobile terminal and a printer is increasingly used to copy a document. For example, image data of a captured image is transmitted from the mobile terminal to the printer and the image is printed by the printer. If a user does not have a multifunction machine having a scanner function and a printer function, the user can copy a document using a mobile terminal and a printer in the above-described manner.
When a user captures an image of a document using a camera function of a mobile terminal, an object adjacent to the document or the user may cast shade on the document. If the user captures an image of the shaded document, the captured image may be shaded. Uneven brightness of the captured image caused by the shade will be referred to as “shade” hereinafter. The readability of the document in the shaded image is low. This leads to a reduction in quality of a printed image.
Japanese Patent Laid-Open No. 2012-95002 discloses a method for correcting shade in a document image captured with a camera. As described in Japanese Patent Laid-Open No. 2012-95002, shade components of the captured image are estimated, and the shade components are removed from the captured image based on information about the estimated shade components. According to this method, to correct shade components of a captured image, a region with a low chroma value and a low lightness value included in the captured image is detected as a character. The character is subjected to correction by a small amount. This eliminates or reduces a likelihood that the character may be corrected such that the character turns bright.
According to the method disclosed in Japanese Patent Laid-Open No. 2012-95002, however, an object in a region that is not detected as a character is subjected to correction for shade component removal regardless of the color of the object. Unfortunately, the shade component removal correction is excessively performed, so that the color of the object turns bright.